#define IN(x,s,g) ((x) >= (s) && (x) < (g))
#define ISIN(x,y,w,h) (IN((x),0,(w)) && IN((y),0,(h)))

#include <cstring>
#include <queue>
#define REP(i,n) for(int i=0; i<(int)(n); i++)

#include <cstdio>
inline int getInt(){ int s; scanf("%d", &s); return s; }

#include <set>

using namespace std;

int d[3000][3000];
char g[3000][3010];

int main(){
  const int h = getInt();
  const int w = getInt();

  REP(i,h) scanf("%s", g[i]);

  memset(d, -1, sizeof(d));
  queue<pair<int, int> > q;

  REP(i,h) REP(j,w) if(g[i][j] == '.') {
    d[i][j] = 0;
    q.push(make_pair(j, i));
  }
  REP(i,h) {
    if(d[i][0] == -1) { d[i][0] = 1; q.push(make_pair(0, i)); }
    if(d[i][w-1] == -1) { d[i][w-1] = 1; q.push(make_pair(w-1, i)); }
  }
  REP(i,w) {
    if(d[0][i] == -1) { d[0][i] = 1; q.push(make_pair(i, 0)); }
    if(d[h-1][i] == -1) { d[h-1][i] = 1; q.push(make_pair(i, h-1)); }
  }

  while (q.size()){
    const auto data = q.front (); q.pop();
    const int x = data.first;
    const int y = data.second;

    REP(i,3) REP(j,3) {
      const int xx = x + i - 1;
      const int yy = y + j - 1;
      if(ISIN(xx, yy, w, h) && d[yy][xx] == -1){
	q.push(make_pair(xx, yy));
	d[yy][xx] = d[y][x] + 1;
      }
    }
  }

  // REP(i,h) { REP(j,w) printf("%02d ", d[i][j]); puts(""); }
  int ans = 0;
  REP(i,h) REP(j,w) ans = max(ans, d[i][j]);
  printf("%d\n", ans);

  return 0;
}